The present invention relates to systems for medical diagnosis and treatment, and specifically to using reference field transducers and medical probes with probe field transducers to detect the position, orientation, or both of the probe within the body of a patient.
There are many medical procedures in which probes, such as catheters, are introduced into the body of a subject or patient. In procedures such as cardiac catheterization and neurosurgery, it is often necessary for the physician or surgeon to know the location of the distal end of the probe inside the body. Although imaging methods such as fluoroscopy and ultrasound are sometimes used for this purpose, they are not always practical or desirable. For example, such systems typically require continuous imaging of the probe and patient during the procedure. In addition, fluoroscopic systems are often undesirable because that they expose the patient and physician to substantial ionizing radiation.
A number of locating systems for detecting the position of a probe or a catheter tip in the body of a patient without the need for continuous imaging of the patient have been proposed. These systems include, for example, those disclosed in U.S. Pat. Nos. 5,558,091; 5,391,199; 5,443,489; and International Patent Publications WO 94/04938 and WO 96/05768, the disclosures of which are hereby incorporated herein by reference. Other electromagnetic tracking systems, not necessarily for medical applications, are described in U.S. Pat. Nos. 3,644,825, 3,868,565, 4,017,858, 4,054,881 and 4,849,692.
Systems such as those disclosed in the ""091, ""199 and ""489 patents and in the ""938 PCT application determine the disposition (i.e., position, orientation, or both) of a probe using one or more field transducers, such as a Hall effect devices, magnetoresistive devices, coils or other antennas carried on the probe. The transducers are typically located at or adjacent the distal end of the probe or at a precisely known location relative to the distal end of the probe. Such systems further utilize one or more reference field transducers disposed outside the body to provide an external frame of reference. The reference field transducers are operative to transmit or detect non-ionizing fields or field components such as magnetic field, electromagnetic radiation or acoustical energy such as ultrasonic vibration. By transmitting fields between the external reference field transducers and the probe field transducers, characteristics of the field transmissions between these devices can be determined and then used to determine the position and orientation of the probe in the external frame of reference.
As described, for example, in the aforementioned ""091 patent, the frame of reference of the external field transducers can be registered with the frame of reference of imaging data such as magnetic resonance imaging data, computerized axial tomographic (xe2x80x9cCATxe2x80x9d) data, or conventional x-ray imaging data, and hence the position and/or orientation data derived from the system can be displayed as a representation of the probe superimposed on an image of the patient""s body. The physician can use this information to guide the probe to the desired location within the patient""s body, and to monitor its location and orientation during treatment or measurement of the internal body structure. This arrangement greatly enhances the ability of the physician to navigate the distal end of the probe through bodily structures and offers significant advantages over conventional methods of navigating probes within the body by feel alone. Because it does not require acquiring an optical image of the surrounding tissues for navigation purposes, it can be used with probes which are too small to accommodate optical elements. These transducer-based systems also avoid the difficulties associated with navigation of a probe by continuous imaging of the probe and patient during the procedure and avoids, for example, prolonged exposure to ionizing radiation inherent in fluoroscopic systems.
Such systems typically utilize reference field transducers or coils which are provided in a fixed, immovable array, in locations such as on the ceiling of an operating room or rigidly fixed to operating or catheterization table. In medical applications, where the system is used to track the location of a probe inside the body of a patient, the coil mounting may interfere with free access by the physician to the patient.
For example, the aforementioned ""938 publication describes a catheter system which uses a plurality of non-concentric coils adjacent to the distal end of the catheter. These coils generate signals in response to externally applied magnetic fields, which allow for the computation of six location and orientation coordinates, so that the disposition of the catheter is known without the need for simultaneous imaging. Preferably, at least three such coils or radiators are arrayed in fixed locations outside the body, adjacent to the area of the body into which the catheter is introduced. For example, in cardiac catheterization, during which the patient is typically supine, three radiators are typically fixedly placed beneath the patient""s thorax, in a fixed coplanar, triangular arrangement, with the centers of the coils from about 2 to 40 cm apart. For detection of the position and orientation of catheters or probes inserted into the brain, the transducers or field radiating coils should desirably be positioned adjacent to the patient""s head. In neurosurgery, however, the patient is often in a seated, upright position or else face-down. Thus, a triangular frame holding the three radiators as described above cannot be comfortably and stably positioned below the head. However, positioning the frame above or beside the head will generally interfere with the surgeon""s manipulation of probes and surgical tools.
It would therefore be desirable to enhance the accuracy and efficacy of probe tracking systems as described above, and other types of systems involving application of electromagnetic or other non-ionizing energy fields to a human body, by adjusting and optimizing the positions of the reference field transducers. Flexibility of placement of the transducers would allow custom positioning of the transducers to move them to the best possible locations to increase sensitivity of the locating system.
One aspect of the present invention provides a system for determining disposition of a probe within the body of a patient. A system in accordance with this aspect of the invention desirably includes a probe having one or more probe field transducers mounted thereon. One or more reference field transducers are also provided. As used in this disclosure, the term xe2x80x9cfield transducerxe2x80x9d encompasses a device which can transmit a non-ionizing field such as a magnetic, electromagnetic, acoustic or optical field and also encompasses a device which can detect one or more components of such a field. In a system according to this aspect of the present invention, the reference field transducers are independently movable with respect to one another and are locatable by the user in desired, user-selected, customizable positions with respect to the body of the patient. Most preferably, the system includes means for mounting the reference field transducers on the body of the patient. In a particularly preferred arrangement, the reference field transducers are mechanically unattached to one another, so that each reference field transducer can be placed in any disposition desired by the user without mechanical constraints imposed by placement of the other reference field transducers. Calibration means are provided for determining the relative dispositions of the field transducers with respect to one another while the reference field transducers are located in the desired positions as, for example, while the reference field transducers are mounted on the patient""s body. As used in this disclosure with reference to a single object, the term xe2x80x9cdispositionxe2x80x9d refers to the position of the object, the orientation of the object, or both. As used in this disclosure with reference to any two objects, the term xe2x80x9crelative dispositionxe2x80x9d refers to the direction from one object to the other, the distance from one object to the other, or both, and also includes the orientation of each object in the frame of reference of the other object. Most preferably, the calibration means is arranged to fully determine all parameters of the relative disposition of the field transducers with respect to one another, so that the distances and directions from each field transducer to each other field transducer, and the orientations of all of the field transducers, are fully known.
The system further includes transmission means to actuate the reference field transducers and probe field transducers so as to transmit one or more non-ionizing fields between the reference field transducers and the probe field transducer or transducers and detect each such transmitted field. For example, in a system where the transmission means actuate the reference field transducers to transmit a magnetic or electromagnetic field, the probe field transducer detects properties of the field received at the probe field transducer or transducers. Calculation means are also provided to determine the disposition of the probe in the frame of reference of the reference field transducers. This calculation proceeds from properties of the detected fields and from the relative dispositions of the reference field transducers with respect to one another.
Because the reference field transducers are independently positionable on or near the patient, they can be placed in an optimum arrangement to provide good sensitivity and signal to noise ratio in the particular area of interest, where a probe must be located during a particular procedure. Also, location of the reference field transducers can be selected to provide unimpeded access for surgical or other medical procedures. As further explained below, the frame of reference defined by the reference field transducers can be registered with the frame of reference of a previously acquired image, and a representation of the probe can be displayed superposed on the previously acquired image. In preferred embodiments where the reference field transducers are mounted on the patient""s body, the frame of reference defined by the reference field transducers moves with the patient. Therefore, registration with a previously acquired image can be maintained without a need for the adjustment or reregistration despite movement of the patient. In systems according to further embodiments of the invention, the calibration means and calculation means are arranged to redetermine the relative dispositions of the reference field transducers periodically and to redetermine the disposition of the probe based upon the redetermined relative dispositions of the reference field transducers. For example, the system may operate cyclically, so that each cycle includes redetermination of the relative dispositions of the reference field transducers as well as determination of the probe disposition. Stated another way, the frame of reference of the reference field transducers is updated before each measurement of probe disposition. Alternatively, the reference field transducer disposition may be updated periodically. These systems permit mounting of the reference field transducers on movable elements of the body as, for example, on the surface of the abdomen or thorax.
The calibration means may include one or more calibration field transducers mounted to one or more of the reference field transducers. Thus, one or more of the reference field transducers is provided in a reference assembly with one or more calibration field transducers. The calibration means is arranged to determine the relative dispositions of the reference field transducers by detecting non-ionizing, fields transmitted to or from the calibration field transducers as, for example, field transmitted from the reference transducers of other reference assemblies.
Further aspects of the present invention provide methods of determining the disposition of a probe within the body of a patient. Methods according to this aspect of the invention desirably include the steps of providing a probe as aforesaid having one or more probe field transducers and positioning a plurality of reference field transducers positionable independently with respect to one another in desired, user-selected customizable positions with respect to the body of the patient. As discussed above in connection with the apparatus, the relative dispositions of the reference field transducers with respect to one another are determined while the reference field transducers are located in their desired positions. The probe is then located by transmitting one or more non-ionizing fields between the probe field transducers and reference field transducers and detecting these fields. The relative disposition of the probe with respect to the reference field transducers is determined from the properties of the detected fields and from the relative dispositions of the reference field transducers with respect to one another. As discussed above in connection with the apparatus, the relative dispositions of the reference field transducers desirably are redetermined frequently.
Still further aspects of the present invention include apparatus for generating or detecting non-Ionizing fields transmitted to or from within the body of a patient. Aspects according to this aspect of the invention includes a plurality of reference field transducers and means for positioning each of the reference field transducers independently with respect to one another in desired, customizable positions in close proximity to the body of a medical patient. Apparatus according to this aspect of the present invention can be utilized in the systems and methods discussed above. The positioning means may incorporate means for securing each reference field transducer to the body of the patient as, for example, adhesive means or other fastening devices which can engage the body. Yet another aspect of the present invention includes a kit incorporating a plurality of separate reference field transducers and means such as adhesives or other fastening devices for securing the reference field transducers to the body of the patient. A still further aspect of the present invention includes a reference field transducer assembly which incorporates a coil or other field transducer that generates heat during operation and a housing structure containing such coil. The assembly has a front surface which lies against the patient during operation and a rear surface. Means are provided in the housing for limiting heating of the front surface by heat generated in the coil. For example, the housing may include thermal insulation disposed between the coil and the front surface and preferably also includes means for dissipating heat within the housing or through the rear surface. These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.